A fuel cell uses hydrogen or hydrogen-rich gas as a fuel and oxygen as an oxidant. The major by-product of the chemical reaction taking place in a fuel cell is water, and generally no other harmful substance is emitted. The energy conversion efficiency of a fuel cell is far higher than that of an internal-combustion engine. Thus, a fuel cell is a safe, reliable, clean, environment-friendly and energy-saving power generator. As the fuel cell technology has been well established, fuel cells have been used in equipments as large as submarines and automobiles, and as small as portable computers and mobile phones.
The cathode of a fuel cell is generally exposed to ambient atmosphere directly or indirectly, so as to catch oxygen as its oxidant. Thus, the cathode of a fuel cell does not need to be sealed, or at least not strictly sealed. On the other hand, the anode gas chamber of a fuel cell has to be sealed since a combustible gas of a certain pressure flows through the chamber.
Chinese patent application No. 99808103.5, assigned to U.S. Manhattan Scientifics Inc., which corresponds to U.S. Pat. No. 6,783,883 and is titled “Gas-Proof Assembly Composed of a Bipolar Plate and a Membrane-Electrode Unit of Polymer Electrolyte Membrane Fuel Cells”, discloses a component composed of a fuel cell bipolar plate used as a structural unit of a fuel cell stack and a membrane electrode unit, wherein the membrane electrode unit comprises a polymer electrolyte membrane above which, except for its periphery, there is a gas diffusing layer in the component, and the bipolar plate lies on one side of the gas diffusing layer opposite the membrane, extending beyond the periphery of the gas diffusing layer, so as to form a side annular volume area defined by the bipolar plate, the gas diffusing layer and the membrane from above, the inner side and the lower side, respectively, characterized by a seamless and hermetical filling of a cured adhesive in the annular volume area up to its boundary surface. FIG. 4 is a schematic view of the component before it is assembled, illustrating the bipolar plate, the adhesive, the gas diffusing layer and the electrolyte membrane.
With simplicity in structure and process as its merits, the above mentioned technical solution suffers from some drawbacks. In practice, there sometimes exist little holes in the adhesive-filling area adjacent to the electrolyte membrane and the gas diffusing layer. When such a fuel cell has been left unused for a long time, the holes will be filled with air. Once the fuel cell is put into use again, the fuel fed into the chamber will react with the air quickly in the presence of the catalyst on the electrolyte membrane surface, producing a relatively high temperature and thus leading to breakthrough and gas-leak of the electrolyte membrane due to burning. Additionally, the adhesive-filled area often needs to be widened in order to enhance the reliability of sealing, so that the electrolyte membrane is wasted inevitably. It is known that the electrolyte membrane and the catalyst adhered therewith are expensive.